CN111521565B - Crack opening width detection system and method based on laser ultrasound - Google Patents

Abstract

The invention discloses a crack opening width detection system and method based on laser ultrasound, wherein the system comprises an ultrasonic excitation device, a detection device and a control device, wherein the ultrasonic excitation device is used as an ultrasonic signal excitation source of a sample with a crack to be detected; the heating device is used for heating the crack to be detected on the sample and generating thermal stress to close the crack; the ultrasonic detection device is used for receiving ultrasonic signals; the signal acquisition device is used for acquiring ultrasonic signals and transmitting the ultrasonic signals to the control device; the moving device is used for driving the heating point of the heating device on the crack to be detected and the crack to be detected to synchronously move; and the control device is used for adjusting the heating power of the heating device and controlling the movement of the movement device, and is also used for calculating the opening width of the crack to be detected on the sample according to the corresponding relation between the displacement generated by the crack closure and the heating power. The invention can realize the detection of the opening width of the fatigue crack when a load is applied, has no damage in the whole detection process, does not influence the detected sample, and has high whole detection efficiency and high precision.

Description

A system and method for crack opening width detection based on laser ultrasound

technical field

The invention belongs to the technical field of non-destructive testing of materials, in particular to the technical field of laser ultrasonic testing, and in particular to a crack opening width detection system and method based on laser ultrasonic.

Background technique

Laser ultrasonic technology is a non-destructive testing technology for materials. It has the characteristics of non-contact, broadband, multi-mode excitation, and easy movement of excitation and detection light sources. It is suitable for the detection of complex components and large components, and is suitable for high temperature and high pressure. , high acid and alkali and radiation and other harsh environments. Books [Wei Kunxia. Non-destructive testing technology [M]. China Petrochemical Press, 2016.] introduced that the currently commonly used laser ultrasonic testing method uses laser beams as excitation to excite ultrasonic signals in the tested material, using piezoelectric transducers Or vibrometer and other methods to receive the signal.

Crack detection is an important aspect of nondestructive testing, and laser ultrasonic crack detection technology is an emerging research hotspot in the direction of crack detection. Books [Shen Zhonghua, Yuan Ling, Zhang Hongchao, etc. Laser Ultrasound in Solids [M]. 1st Edition. Beijing: People's Posts and Telecommunications Press, 2015.] Introduced that the linear laser ultrasonic crack detection method detects the interaction between ultrasonic waves and cracks. However, if the opening width of the crack is further reduced, the surface wave will directly pass through the crack without reflection and scattering, so it cannot effectively detect such micro-cracks. The nonlinear laser ultrasonic crack detection method uses the change of the crack closure state and various nonlinear acoustic phenomena caused by it to detect real micro-cracks with a small opening width. Compared with the traditional linear laser ultrasonic detection method, its outstanding The advantage is that the detection sensitivity to real micro-cracks can be greatly improved and enhanced.

Changes in crack closure under applied loads can also be detected using nonlinear laser ultrasonic methods. Chinese patent 201110185407.2 discloses a non-destructive detection method for fatigue cracks on the surface of solid materials. During each step of the scanning process of the scanning light source, the detection of micro-cracks is realized by detecting the change of the surface acoustic wave signal excited by the excitation light source under the conditions of laser heating and cooling. Previously, some scholars [Lv Jinchao, Shen Zhonghua, Ni Chenyin. Laser ultrasonic monitoring of photo-induced crack closure and change [J]. Nondestructive Testing, 2017,39(6):19-23.] passed through the black glass sample under the condition of transmission The detection of surface waves and mode conversion signals to study the crack modification during photo-induced crack closure. This scheme can detect the change of the crack closure under the applied load, and the process is simple, but there are still the following shortcomings: the data in the acquisition system is highly random, and it is difficult to detect the crack opening width.

Contents of the invention

The object of the present invention is to provide a crack opening width detection system and method based on laser ultrasound to address the above-mentioned deficiencies in the prior art.

The technical solution to realize the object of the present invention is: a crack opening width detection system based on laser ultrasound, the system includes a sample with a crack to be measured, an ultrasonic excitation device, a heating device, an ultrasonic detection device, a signal acquisition device, a moving devices and controls;

The ultrasonic excitation device is used as an excitation source of ultrasonic signals for samples with cracks to be tested;

The heating device is used to heat the crack to be tested on the sample to generate thermal stress to close the crack;

The ultrasonic detection device is used to receive ultrasonic signals;

The signal acquisition device is used to collect ultrasonic signals and transmit them to the control device;

The moving device is used to drive the heating point of the heating device on the crack to be tested to move synchronously with the crack to be tested;

The control device is used to adjust the heating power of the heating device and control the movement of the moving device, and is also used to obtain the opening width of the crack to be measured on the sample according to the corresponding relationship between the displacement generated by the crack closure and the heating power;

The excitation point where the ultrasonic excitation device irradiates the surface of the sample, the heating point where the heating device irradiates the crack to be tested, and the detection point where the ultrasonic detection device performs ultrasonic detection are located on the same straight line, and the straight line is on the same line as the crack to be tested. Go vertical.

Further, the heating device specifically adopts a continuous laser.

Further, the system further includes a reflection device, which is arranged on the moving device together with the sample, and the emitted light of the continuous laser is reflected by the reflection device and then irradiates the crack to be tested on the sample.

A detection method based on a laser ultrasonic crack opening width detection system, the method comprising the following steps:

Step 1, determining the heating area of the heating device on the crack to be tested;

Step 2, adjust the ultrasonic excitation device to irradiate the excitation point on the sample surface with the crack to be tested, the heating device to irradiate the heating point on the crack to be tested, and the detection point of the ultrasonic detection device for ultrasonic detection to be on the same straight line, and the The straight line is perpendicular to the direction of the crack to be tested, and then the ultrasonic excitation device and the ultrasonic detection device are fixed;

Step 3, the heating point of the heating device on the crack to be tested and the crack to be tested are driven by the moving device to move synchronously along the direction of the crack to be tested, so that the ultrasonic excitation device and the ultrasonic detection device are from one side of the heating area Move to the other side, and the ultrasonic signal is collected by the signal acquisition device and transmitted to the control device;

Step 4, setting the initial heating power of the heating device;

Step 5, turn on the heating device, heat the crack to be tested to close the crack through thermal stress, and after reaching a thermal equilibrium state, perform a scan and signal acquisition according to the process of step 3; turn off the heating device to restore the crack to be tested to the equilibrium state at room temperature, Then follow the process of step 3 again to realize a scan and signal acquisition;

Step 6, preset the step sequence, gradually increase the heating power according to each step in the sequence, and repeat step 5;

Step 7, obtaining the heating power of the heating device when the crack to be measured in the scanning area is completely closed after the above process, that is, when the ultrasonic signal is saturated;

Step 8, according to the corresponding relationship between the displacement generated by crack closure and the heating power, combined with the heating power in step 7, using the control device to obtain the displacement generated when the crack to be measured in the scanning area is completely closed, that is, the scanning area The opening width of the inner crack to be tested.

Further, the method further includes performing before step 7: extracting the peak-to-peak value of the ultrasonic signal in each scan.

Further, the corresponding relationship between the displacement generated by the crack closure described in step 8 and the heating power is specifically:

In the formula, Δd is the displacement caused by crack closure, R is the reflection coefficient of the sample surface, P is the heating power, β is the linear thermal expansion coefficient of the sample, and k is the thermal conductivity of the sample; for the heating device, a continuous laser is used, f( t) is the time modulation function of the laser.

Compared with the prior art, the present invention has the following significant advantages: 1) The traditional nonlinear laser ultrasonic technology detects the change of the crack closure under the applied load, and what is obtained is a single crack in the heating region during the crack closure process. The ultrasonic signal changes at the position, the invention makes the ultrasonic excitation device and the ultrasonic detection device move from one side of the heating area to the other side through the synchronous movement of the heating point on the crack to be tested and the crack to be tested along the direction of the crack, and the obtained It is the ultrasonic signal change at multiple positions in the heating region during the crack closure process, which can realize the detection of the opening width of the fatigue crack when the load is applied; 2) the present invention uses laser ultrasonic technology to achieve the purpose of detecting the crack opening width, and the entire detection process 3) the detection efficiency is high and the precision is high; 4) the present invention obtains the heating power of the heating device when the crack to be measured in the scanning area is completely closed, that is, when the ultrasonic signal is saturated, and according to the crack closure The corresponding relationship between the generated displacement and the heating power is obtained by using the control device to obtain the opening width of the crack to be tested in the scanning area. The operation is simple, the repeatability is good, and the result is stable.

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is a schematic structural diagram of a crack opening width detection system based on laser ultrasound in an embodiment.

Fig. 2 is a scanning result diagram of the peak-to-peak value of the transmitted surface wave signal obtained when the middle part of a certain crack is in a heated state in one embodiment, the abscissa represents the scanning steps of the excitation-detection source, the ordinate represents the heating power, and the pixels are gray The degree value represents the peak-to-peak value of the ultrasound signal.

Fig. 3 is a scan result diagram of the peak-to-peak value of the transmission mode conversion wave signal obtained when the middle part of a certain crack is in a heated state in one embodiment, the abscissa represents the number of scanning steps of the excitation-detection source, the ordinate represents the heating power, and the pixel The gray value represents the peak-to-peak value of the ultrasound signal.

Fig. 4 is an atomic force microscope (AFM) image at the middle of a certain crack in one embodiment.

detailed description

In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, not to limit the present application.

In one embodiment, with reference to Fig. 1, a crack opening width detection system based on laser ultrasound is provided, the system includes a sample 4 with a crack to be measured, an ultrasonic excitation device 1, a heating device 2, an ultrasonic detection device 3, Signal acquisition device 5, motion device 6 and control device 7;

The ultrasonic excitation device 1 is used as an excitation source of an ultrasonic signal for a sample 4 with a crack to be tested;

The heating device 2 is used to heat the crack to be tested on the sample 4 to generate thermal stress to close the crack;

The ultrasonic detection device 3 is used to receive ultrasonic signals;

The signal acquisition device 5 is used to collect ultrasonic signals and transmit them to the control device 7;

The moving device 6 is used to drive the heating point of the heating device 2 on the crack to be tested to move synchronously with the crack to be tested;

Exemplarily here, the moving device 6 may adopt a stepping motor.

The control device 7 is used to adjust the heating power of the heating device 2 and control the movement of the moving device 6, and is also used to obtain the opening of the crack to be measured on the sample 4 according to the corresponding relationship between the displacement generated by the crack closure and the heating power width;

Exemplarily here, the control device 7 may be a computer and other computing control devices.

The excitation point irradiated by the ultrasonic excitation device 1 to the surface of the sample 4, the heating point irradiated by the heating device 2 to the crack to be measured, and the detection point for ultrasonic detection by the ultrasonic detection device 3 are located on the same straight line, and the straight line is in line with the The direction of the crack to be tested is vertical.

Here, the ultrasonic excitation device 1 and the ultrasonic detection device 3 are located on the same side or different sides of the crack to be detected, and the ultrasonic detection device 3 receives reflected or transmitted ultrasonic signals.

The system proposed by the present invention can detect any width and any type (uniform width, uneven width) on solid material samples; for uniform width, a certain crack area can be detected; for uneven width, point-by-point scanning can be performed Detection) crack opening width for detection, wide applicability.

Further, in one of the embodiments, the heating device 2 specifically adopts a continuous laser.

Further, in one of the embodiments, the system also includes a reflection device, which is set on the moving device 6 with the sample 4, and the output light of the continuous laser is reflected by the reflection device and irradiates the sample 4 cracks to be tested.

Adopting the scheme of this embodiment, the heating device 2 can be fixed, the shaking caused by directly driving the heating device 2 can be prevented, the stability of irradiated light can be improved, the damage to the heating device 2 can be reduced, and its service life can be extended.

Further, in one of the embodiments, the center of the light spot formed on the crack to be tested by the emitted light of the continuous laser coincides with the center of the crack to be tested along the crack width direction.

By adopting the solution of this embodiment, the light energy of the continuous laser can be fully utilized, and a better irradiation effect can be achieved.

Further, in one of the embodiments, the ultrasonic excitation device 1 adopts a pulsed laser, and the pulsed laser emitted by it is focused into a point light source and irradiated on the surface of the sample 4 to excite ultrasound.

Further, in one of the embodiments, the ultrasonic detection device 3 adopts a continuous laser or an acoustic transducer.

In one embodiment, a method for detecting crack opening width based on laser ultrasound is provided, the method comprising the following steps:

Step 1, determining the heating area of the heating device 2 on the crack to be tested;

Step 2, adjust the ultrasonic excitation device 1 to irradiate the excitation point on the surface of the sample 4 with the crack to be tested, the heating device 2 to irradiate the heating point on the crack to be tested, and the detection point of the ultrasonic detection device 3 for ultrasonic detection to be located at the same a straight line, and the straight line is perpendicular to the direction of the crack to be tested, and then the ultrasonic excitation device 1 and the ultrasonic detection device 3 are fixed;

Step 3, the heating point of the heating device 2 on the crack to be tested is driven by the moving device 6 and the crack to be tested moves synchronously along the direction of the crack to be tested, so that the ultrasonic excitation device 1 and the ultrasonic detection device 3 start from the heating One side of the area moves to the other side, and the ultrasonic signal is collected by the signal acquisition device 5 and transmitted to the control device 7;

Step 4, setting the initial heating power of the heating device 2;

Step 5, turn on the heating device 2, heat the crack to be tested to close the crack through thermal stress, and after reaching the thermal equilibrium state, follow the process of step 3 to realize a scan and signal acquisition; turn off the heating device 2 to restore the crack to be tested to the balance at room temperature state, and then follow the process of step 3 again to realize a scan and signal acquisition;

Step 6, preset the step sequence, gradually increase the heating power according to each step in the sequence, and repeat step 5;

Step 7, obtaining the heating power of the heating device 2 when the crack to be measured in the scanning area is completely closed after the above process, that is, when the ultrasonic signal is saturated;

Step 8, according to the corresponding relationship between the displacement generated by crack closure and the heating power, combined with the heating power in step 7, using the control device 7 to obtain the displacement generated when the crack to be measured in the scanning area is completely closed, that is, the scanning The opening width of the crack to be tested in the area.

Further, in one of the embodiments, the method further includes performing before step 7: extracting the peak-to-peak value of the ultrasonic signal in each scan.

By adopting the solution of this embodiment, the calculation amount of step 7 can be reduced.

Further preferably, in one of the embodiments, the step values in the step sequence in step 6 are all the same.

Adopting the solution of this embodiment facilitates adjustment and reduces complexity.

Further, in one of the embodiments, the corresponding relationship between the displacement generated by the crack closure and the heating power in step 8 is specifically:

In the formula, Δd is the displacement caused by crack closure, R is the reflection coefficient of the sample surface, P is the heating power, β is the linear thermal expansion coefficient of the sample, and k is the thermal conductivity of the sample; for the heating device, a continuous laser is used, f( t) is the time modulation function of the laser, if it is other heating sources, f(t) is the time modulation function of the heating source.

Here, for other specific limitations on each step of the above-mentioned detection method, please refer to the above-mentioned limitations on the crack opening width detection system based on laser ultrasound, which will not be repeated here.

As a specific example, in one of the embodiments, the laser ultrasonic-based crack opening width detection system and method of the present invention are further verified and described. In this embodiment, the sample with cracks used is a black glass sample, and its material parameters are approximately as follows: surface reflection coefficient R=0.04, thermal conductivity k=1.38W/m K, linear thermal expansion coefficient β=7.5× 10 ^-7 /K. The crack to be measured in this embodiment is somewhere in the middle of the crack on the black glass sample. For the black glass sample, the heating optical power of 300mW is enough to completely close the crack in the middle and the tip of the crack, and 20s is enough to stabilize the crack state. The heating device 2 adopts a continuous laser with a wavelength of 532nm, the ultrasonic excitation device 1 adopts a pulsed laser with a wavelength of 1064nm, and the ultrasonic detection device 3 adopts a continuous laser with a wavelength of 638nm. opposite side. The specific verification process includes:

(1) Determine the heating area of the heating device 2 on the crack to be tested.

(2) Adjust the excitation point where the ultrasonic excitation device 1 irradiates to the surface of the sample 4 with the crack to be measured, the heating point where the heating device 2 irradiates the crack to be measured, and the detection point where the ultrasonic detection device 3 performs ultrasonic detection are located at the same and the straight line is perpendicular to the direction of the crack to be tested, and then the ultrasonic excitation device 1 and the ultrasonic detection device 3 are fixed.

(3) Drive the heating point of the heating device 2 on the crack to be tested and the crack to be tested to move synchronously along the direction of the crack to be tested by the moving device 6, so that the ultrasonic excitation device 1 and the ultrasonic detection device 3 are heated from the One side of the area moves to the other side, and the ultrasonic signal without heating is collected by the signal acquisition device 5 and transmitted to the control device 7; at the beginning of scanning, the distance between the heating source and the straight line formed by the excitation-detection source is about 150 μm, and the scanning step length is 30μm, the scanning range is 300μm.

(4) Set the initial heating power of the heating device 2 to 10 mW.

(5) Turn on the heating device 2, heat the crack to be tested to close the crack through thermal stress, and after reaching the thermal equilibrium state, realize a scan and signal acquisition according to the above process 3; turn off the heating device 2 to restore the crack to be tested to the equilibrium state at room temperature , and then implement a scan and signal acquisition according to the above-mentioned process 3 again.

(6) Preset the step length sequence, gradually increase the heating power according to each step length in the sequence, and repeat the above process 5, and close the crack through thermal stress; wherein, the step length values in the step length sequence are equal to The maximum heating power is 10mW, which can be increased to 300mW.

(7) Extracting the peak-to-peak value of the collected scanning ultrasonic signal, drawing a scanning map, and obtaining the heating power of the heating device 2 when the crack to be tested in the scanning area is completely closed after the above process, that is, when the ultrasonic signal is saturated. It can be seen from Figures 2 and 3 that when the heating optical power increases to about 200mW, as the heating optical power increases, the peak value of the transmission surface in Figure 2 remains basically unchanged and the black area gradually disappears, and the mode conversion peak in Figure 3 The peak value is approximately 0, which indicates that the crack at the opening width to be measured has reached a completely closed state under the heating light power of 200mW.

(8) According to the corresponding relationship between the displacement generated by the crack closure and the heating power, combined with the heating power obtained in the above process 7, the displacement generated when the crack to be measured in the scanning area is completely closed, that is, the crack to be measured in the scanning area The opening width of is:

The width of the crack to be measured is observed by an atomic force microscope (AFM), as shown in Fig. 4 . Comparing Fig. 4 with the calculation results of the present invention, it can be seen that the crack width measured by the present invention is basically consistent with the actual measured width.

The technical features of the above embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be It is considered to be within the range described in this specification.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements are possible, which fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. a crack opening width detection system based on laser ultrasonic, it is characterized in that, described system comprises sample (4) with crack to be measured, ultrasonic excitation device (1), heating device (2), ultrasonic detection device ( 3), signal acquisition device (5), motion device (6) and control device (7); The ultrasonic excitation device (1) is used as an excitation source of an ultrasonic signal for a sample (4) with a crack to be tested; The heating device (2) is used to heat the crack to be measured on the sample (4) to generate thermal stress to close the crack; The ultrasonic detection device (3) is used for receiving ultrasonic signals; The signal acquisition device (5) is used to collect ultrasonic signals and transmit them to the control device (7); The moving device (6) is used to drive the heating point of the heating device (2) on the crack to be tested to move synchronously with the crack to be tested; The control device (7) is used to adjust the heating power of the heating device (2) and control the movement of the moving device (6), and is also used to calculate the sample ( 4) The opening width of the crack to be measured; The ultrasonic excitation device (1) irradiates the excitation point on the surface of the sample (4), the heating device (2) irradiates the heating point on the crack to be tested, and the detection point of the ultrasonic detection device (3) for ultrasonic detection is located at the same straight line, and the straight line is perpendicular to the direction of the crack to be tested. 2. The crack opening width detection system based on laser ultrasound according to claim 1, characterized in that, the heating device (2) specifically adopts a continuous laser. 3. the crack opening width detection system based on laser ultrasonic according to claim 2, is characterized in that, described system also comprises reflection device, and this device and sample (4) are all arranged on the moving device (6), and described The outgoing light of the continuous laser is reflected by the reflecting device and irradiates the crack to be measured on the sample (4). 4. The crack opening width detection system based on laser ultrasound according to claim 3, characterized in that, the center of the light spot formed by the outgoing light of the continuous laser on the crack to be measured is in the same direction as the crack to be measured along the crack width direction. The centers coincide. 5. The crack opening width detection system based on laser ultrasound according to claim 1, wherein the ultrasonic excitation device (1) adopts a pulse laser, and the pulse laser emitted by it is focused into a point light source to irradiate the sample The surface of (4) excites ultrasound. 6. The crack opening width detection system based on laser ultrasound according to claim 1, characterized in that the ultrasonic detection device (3) adopts a continuous laser or an acoustic transducer. 7. Based on the detection method of the crack opening width detection system based on laser ultrasound according to any one of claims 1 to 6, it is characterized in that the method comprises the following steps: Step 1, determining the heating area of the heating device (2) on the crack to be tested; Step 2, adjust the ultrasonic excitation device (1) to irradiate the excitation point on the surface of the sample (4) with the crack to be tested, the heating device (2) to irradiate the heating point on the crack to be tested, and the ultrasonic detection device (3) The detection points for ultrasonic detection are located on the same straight line, and the straight line is perpendicular to the direction of the crack to be tested, and then the ultrasonic excitation device (1) and the ultrasonic detection device (3) are fixed; Step 3, the moving device (6) drives the heating point of the heating device (2) on the crack to be tested and the crack to be tested to move synchronously along the direction of the crack to be tested, so that the ultrasonic excitation device (1) and the ultrasonic detection The device (3) moves from one side of the heating area to the other side, and the ultrasonic signal is collected by the signal collection device (5) and transmitted to the control device (7); Step 4, setting the initial heating power of the heating device (2); Step 5, turn on the heating device (2), heat the crack to be tested to close the crack through thermal stress, and after reaching a thermal equilibrium state, perform a scan and signal acquisition according to the process of step 3; turn off the heating device (2) to recover the crack to be tested The equilibrium state at room temperature, and then follow the process of step 3 again to achieve a scan and signal acquisition; Step 6, preset the step sequence, gradually increase the heating power according to each step in the sequence, and repeat step 5; Step 7, obtaining the heating power of the heating device (2) when the crack to be measured in the scanning area is completely closed after the above process, that is, when the ultrasonic signal is saturated; Step 8, according to the corresponding relationship between the displacement generated by crack closure and the heating power, combined with the heating power in step 7, using the control device (7) to obtain the displacement generated when the crack to be measured in the scanning area is completely closed, That is, the opening width of the crack to be tested in the scanning area. 8 . The laser-ultrasonic-based crack opening width detection method according to claim 7 , characterized in that, the method further comprises performing before step 7: extracting the peak-to-peak value of the ultrasonic signal in each scan. 9. The method for detecting crack opening width based on laser ultrasound according to claim 7, characterized in that the step values in the step sequence in step 6 are all the same. 10. The crack opening width detection method based on laser ultrasound according to claim 7, characterized in that the corresponding relationship between the displacement generated by the crack closure described in step 8 and the heating power is specifically:

In the formula, Δd is the displacement caused by crack closure, R is the reflection coefficient of the sample surface, P is the heating power, β is the linear thermal expansion coefficient of the sample, and k is the thermal conductivity of the sample; for the heating device, a continuous laser is used, f( t) is the time modulation function of the laser.

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